Radio receiving system



6, 1940- K. A. CHITTICK ET AL 2,209,959

RADIO RECEIVING SYSTEM Filed March 51, 1938 .2 Sheets-Sheet 1 attorney Aug. 6, 1940. K. A. cHrrTlcK ET AL RADIO RECEIVING SYSTEM Filed March 31, 1938 2 Sheets-Sheet 2 V 2 M0 k K JQ il if] Patented Aug. 6, 1940 UNITED STATES PATENT OFFICE RADIO RECEIVING SYSTEM ware Application March 31, 1938, Serial No. 199,106

6 Claims.

The present invention relates to radio receiving systems and more particularly to receiving systems of the superheterodyne type, comprising a tunable oscillator circuit and a tunable It is an object of the present invention to provide a radio receiving system of the type above referred to which may be tuned variably through a predetermined tuning range and which 15 may be tuned selectively to any one of a plurality of preselected signal frequencies within or without that tuning range. In applying this system to broadcast receivers, the system is tunable throughout the broadcast 6 range by variable tuning means and is also arranged to be preadjusted for response in a plu-, rality of selectable points at differing frequencies within that tuning range, whereby the receiving system may be made to respond to a plurality 25 of preselected signal channels or broadcasting stations instantly by push-button or similar control means for switching into circuit various preadjusted tuning elements.

The preadjusted tuning elements for oscilla- 30 tor and signal receiving circuits of a superheterodyne receiver provided by the present invention permit a further object of the invention to be carried out in that the circuits for preselection of a plurality of signal channels are 35 simplified and adapted for compact mounting within a receiver chassis with the adjustment means grouped for ready adjustment in one 10- cation.

In providing for the control of a preselection 40 system, consideration must be given to stability of operation over long periods of time without additional adjustment of the pretuned circuit elements, and a simplification of the switching operations involved. Accordingly, it is a further 45 object of the present invention to provide an improved radio receiving circuit of the type referred to wherein the selective switchingoperations may be simplified and stability of operation may be improved.

50 'It is also an object of the present invention to provide a superheterodyne radio receiving system having simple means for presetting the same for response in a plurality of preselected signal channels and for automatically tuningsaid 55 system to each of said preselected channels automatically upon operation of any one of a plurality of push-button controls or other suitable selecting means in connection with a simplified circuit arrangement therefor.

The invention will, however, be better understood from the following description, when considered in connection with the accompanying drawings, and its scope will be pointed out in the appended claims.

In the drawings- Figure 1 is a schematic circuit diagram of a radio receiving system embodying the invention, and

Figure 2 is a similar schematic circuit diagram of a radio receiving system embodying the invention and provided with a modification oi the selective switching system shown in connection with Fig. 1.

Referring to Fig. l, the receiving system, of the superheterodyne type, is provided with a signal input or receiving circuit 5-6 in which there is connected the tunable secondary winding 1 of a signal input or antenna coupling transformer 8, the primary 9 of which is coupled to an antenna and ground system It, II for 001- lecting and receiving signals.

The low potential side of the signal input circuit 6 may be grounded to the chassis as indicated and the high potential side 5 is connected to the control grid l2 of a combined first detector and oscillator tube l3 through the usual coupling capacitor 14 and grid resistor 15.

The tube I 3 is provided with a screen grid 15, an output anode H, the latter being connected with an output anode circuit l8 and with the tuned primary IQ of an intermediate frequency amplifier input transformer 20, which may be coupled through the tuned secondary 2| to the usual intermediate frequency amplifier (not shown), and the remainder of the receiving system, which does not concern the invention and is therefore not illustrated.

While any suitable oscillator may be utilized,- in the present example, the oscillator tube elemerits are included within the tube l3 and comprise a cathode 22 in common with the detector, a grid element 23 functioning as a plate for the oscillator, and a control grid 24 located between the cathode and the grid element 23, the

grid 24 being connected back to cathode through the usual grid resistor 25, as shown.

The oscillator is preferably of the feedback coil type employing tuned grid circuits and anode circuit feedback coupling thereto. In the present example, the oscillator anode electrode 23 tor grid circuit inductances, indicated at 4|-45,'

inclusive, certain of which are tuned by means of adjustable cores 46 of magnetic material and one of which, 45, is tunable by means of a variable tuning capacitor section, indicated at 41, in shunt therewith, together with a trimmer capacitor, indicated at 48.

The various grid circuit inductances are returned to the cathode 22 which is grounded, as indicated at 49, through a ground connection, indicated at 56.

In step with the switch section 21 and the movable contact element 29 thereof, is a second movable contact element 5| in a second section 52 of the switch, which serves to connect the grid circuit of the oscillator through the grid capacitor 53 and a connecting lead 54 selectively with the inductances 4|-45, inclusive, through a fixed contact 55 connected with the lead 54 and engaging the contact 5|, and a series of fixed contacts 56-60, inclusive, for the successive inductances 4|-45, respectively.

In the positions shown in the drawings, the switch elements 29 and 5| provide a grid connection for the oscillator grid 24 through the contacts 55 and 56 with the inductance 4| which is adjustable by the core 46 to any predetermined frequency within a selected range of signal frequencies, such as the standard broadcast band, differing therefrom by the amount of the desired intermediate frequency, and the anode circuit 26 is coupled to this inductance through the connections provided by the contacts 28 and 36 and the feedback winding 35, which is coupled to the winding 4| as indicated.

The oscillations established on the oscillator grid 24 are electronically coupledto the oscillations supplied by the signal receiving circuit to the first detector or mixer grid l2, and the resulting intermediate frequency is transferred through the output circuit |8 to the intermediate frequency amplifier through the coupling provided by the tuned coupling means20.

Each of the othersof the plurality of tuning inductances 42-44, inclusive, are similarly adjusted to provide oscillator frequenc es for heterodyning predetermined signals to the desired intermediate frequency, by means of the adjustable cores, while the inductance is variably tunable by the variable capacitor section 41 throughout a predetermined range, such as the entire broadcast range for manually tuning the receiver.

For tuning the signal input circuit, a third section 6|, of the selector switch, is provided with a movable contact element 62 in connection with a fixed contact 63 for the high potential side 5 of the signal input circuit, and a series of fixed contacts 64-68 for selective connection with the movable contact 62 to place in shunt with the circuit 5-6 and the secondary winding or inductance element I one of a series of adjustable capacitors 69-12, inclusive, and a manually variable tuning capacitor section 13 having a shunt trimmer capacitor 14.

As shown in the drawings, the switch section 62 provides connection for the capacitor 69 in shunt with the winding 1 to tune the signal input circuit to a signal channel or broadcasting station, the frequency of which beats with the then adjusted oscillator frequency established by the winding 4| and the feedback winding 35 to produce the desired intermediate frequency for receiving that signal channel or station.

The switch sections 29, 5| and 62 are interconnected as indicated by the dotted connection 15 to move progressively step by step through the successive contacts, from the initial positions shown through the contacts consecutively and in step, whereby a plurality of preselected broadcasting stations or signal channels may be received by thesystem in accordance with the adjustment of the selector switch, and with the final step, in this case the fifth, providing for manually tuning the receiving system throughout the broadcast band or other selected frequency band by means of the variable capacitors 13 and 41. As in the usual receiving system the capacitors 13 and 41 are interconnected for joint control as indicated by the dotted connection 16.

In this receiver arrangement, the adjustable capacitors 69-12 for the signal input circuit or first detector and the adjustable inductances 4l-43 for the oscillator circuit, are arranged in close spaced relation to each other in a convenient location on the receiver chassis for adjustment all at one time. It will be seen that this may be done for the reason that the adjusting means for the oscillator, while comprising small inductance elements, does not require shielding from and' may be located adjacent to the tuning adjustment elements of the input circuit which are ofa different type, being capacitors and not adapted for'inductive coupling with the induct ance elements of the oscillator when positioned adjacent thereto in such a manner as to make the tuning adjustment for both circuits available at one place on the chassis. It should be understood that the spacing of the tuning elements for the two circuits is normally sufficient to prevent stray capacity coupling as is the usual case with the various circuit components in a usual radio receiver chassis. The inductive coupling, however, is prevented since the inductance tuning control elements are utilized only in the oscillator circuit for stabilizing tuning thereof. In other words, the normal spacing between the elements in the group with the usual mounting arrangements for such elements is beyond the limit for any stray capacity coupling as has been found in the construction and operation of the system shown. The provision of capacity tuning adjustment in one circuit andinductive tuning adjustments in the other circuit inherently precludes inductive coupling.

This clearly simplifies the tuning system, the adjusting means and the receiver assembly and permits the system to be applied to small low cost receivers.

It will further be noted that the adjusting means for the oscillator comprising the cores 46, are located at the grounded ends thereof and the adjustment thus does not disturb the coupling between the inductances and the feedback windings therefor and the adjusting operation does not appreciably affect the tuning. Likewise, the capacitors 69-12, inclusive, are adjusted in connection with the grounded electrode thereof as it will be noted that these capacitors are all connected at one electrode in parallel, to chassis or ground, as indicated at IT.

From the foregoing description, it will be seen that in a superheterodyne receiving system, the signal receiving and oscillator circuits may be arranged for simplified switching and adjustment to provide manual tuning, and in addition, automatic or preselection tuning, by changing the circuit tuning elements of the signal receiving circuit and oscillator, which elements, in the one, are capacitive and, in the other, are inductive, whereby the capacitive and inductive elements may be associated sufficiently close together for adjustment at one place without undesired coupling effects as hereinbefore referred to. Furthermore, in the tuning of the oscillator circuits by means of separate inductances having movable magnetite cores for each individual wave band in the tuning range to be preselected, permanent tuning adjustment may be obtained and accurate alignment of the receiving system to the desired signal frequencies may be obtained.

The switching device is shown diagrammatically in one of its simplified forms as comprising three movable elements, one for changing the capacitors in connection with the signal input circuit, another for changing the oscillator tuning inductances in the grid circuit of the oscillater, and a third for changing the feedback windings associated with the oscillator tuning inductances. v

To these elements may be added other switching elements for additional purposes in the receiver, such, for example, as the addition of a trimmer or additional tuning capacitor indicated at 80, for the oscillator grid circuit, which is connected to the circuit lead 54 through a switch section 8| comprising a fixed contact 82 with which there is associated a movable contact element 83 selectively connectable to fixed contacts 84 in parallel. The contacts 84 are connected with the capacitor 80 which is grounded as indicated at 85, thereby placing it in parallel with the successive inductances 4| to 44, inclusive.

In the fifth position of the switch, the contact 86 is left open circuited in orderthat the variable tuning capacitor 41 and the trimmer capacitor 48 may become effective to control the tuning independently of the capacitor 80. The switch section 8i is uni-controlled with the other sections by placing the movable element 93 in connection with the other elements, as indicated by the dotted connection with the line 15.

In addition, pilot lamps 88 or other suitable indicating means may be provided for indicating the various signal channels or stations and the manual tuning position through the operation of a fifth switch section 89, the movable contact element 99 of which is uni-controlled with the others and serves to connect low voltage supply leads indicated at 9| successively through the indicating lamps, as the contact element 90 moves in connection with a fixed contact contact with additional fixed contacts 93 provided for the separate lamp circuits.

Referring now to Fig. 2, the same preselection tuning system may be employed in a superheterodyne receiver adapted for multiple wave band signal reception. This is shown, by way of example, as a system for receiving signals in three difi'ering wave bands, such as the standard broadcast band at present used and a medium and a short band wave. together with means for presetting the signal or broadcasting station selection automatically in one of the wave bands such as the standard broadcast band.

As is customary in multiple wave band receivers, a wave band selector switch is provided in connection with the inductance and capacity tuning elements of both the oscillator and the r-f or first detector circuits.

In the present example, the wave band selector switch comprises two interconnected sections 90, Si for the r---; or signal input circuits and the oscillator circuits, respectively, the first being to provide switching connections with rf inductance units comprising coils 92, 93, 94 and 95 for the signal input or grid circuit 96 and signal input grid 91 of a combined first detector and oscillator tube 93.

The output circuit of this device indicated at 99, is connected through an intermediate frequency amplifier input transformer Hill withan intermediate frequency amplifier indicated at IOI. The input grid 97 is shielded by a screen grid in! from the oscillator anode electrode 593, oscillator grid l 99 and the common cathode M5. The signal input or grid circuit 96 for the first detector is connected through a fixed contact I06, a movable contact element l! and a second fixed contact H38 in the switch section 90, to the high potential terminal I09 of the coil system 93-94, as indicated by the lead H0. A tap Ill on the coil system is connected with a fixed contact H2 and through a movable contact element H3 and a fixed contact H4 is grounded to complete an antenna or signal input circuit H to ground through the winding 92, for which the secondary becomes the windings 93 and 94 in the grid circuit 96 of the detector 98.

In this position, the switch section 90 provides connections for tuning the receiving system auto- -matically to preselected broadcasting stations or signal channels by means of a plurality of adjustable tuning capacitors H6 connected in parallel relation and selectively rendered effective across the signal input circuit 96 and the secondary inductances 93 and 94, through individual push button selector switches I I1. These are connected in parallel to a control lead H8 and with a fixed contact H9 of the switch section 99.

The switch arrangement is such that, as the switch contact element i0! is moved to change connections. in the direction of the arrow on the drawings, the contact I I9 is open circuited, thereby disconnecting the push button tuning elements 6-4 I! and replacing it with the main tuning variable capacitor and shunt trimmer capacitor indicated at I 20 and I'll, respectively. The last named connection is made to a fixed contact I22 which engages the movable contact lll'l as soon as it disengages from the contact H9. It will be seen that, as the switch is moved one step in the direction of the arrow. the remaining connections are unchanged, whereby the tuning system may be operated continuously variable throughout the W eds-est band by the variable tuning capacitor I20.

Successive operations of the switch 90 in the direction of the arrow serve to render effective in circuit as tunable secondary windings, the coils 94 and 95 for the intermediate and short wave bands. and as this does not concern the present invention, no further description thereof is believed to be necessary.

Conjointly operable with the switch section 90. the switch section 9| of the range selector switch controls the oscillator circuits in a similar manner, serving to disconnect the oscillator grid circuit, indicated at I 25, from the connection or control lead indicated at I28, for a bank of parallel tuning inductances I21 and individual selector switches I20 therefor. When the switch SM is moved from the position shown to the' next position, for manual or variable tuning through thebroadcast band, this grid connection is made through a fixed contact in the switch section 9I, as indicated at I29, a movable contact element I30 and a fixed contact I3I.

When the switch 9| is moved for manual tuning in the broadcast and the successive wave bands, the contact I3I is broken with the movable contact element I30 and is established between the contact element I30 and a fixed contact I32 for the main variable tuning capacitor for the oscillator as indicated at I33. This is arranged for uni-control operation with the tuning capacitor I20. Successive positions of the switch section 9| serves to render the oscillator efiective for tuning in the medium and short wave bands and, since this does not concern the present invention, further description is believed to be unnecessary.

It should be noted that the oscillator anode circuit indicated at I34 is connected through a series of feedback windings I35, I36 and I31 and that the winding I31 is coupled to an inductance winding I38 which is connected with the contact I3I and the lead I26 for the preselection tuning system whereby feedback for preselection in any of the several channels arranger to be selected is provided by the single coil I38 at all times through feedback from the coil I31. This arrangement eliminates the necessity for switching in separate feedback windings as in the preceding embodiment of the invention shown in Fig. 1. In this arrangement, the inductance elements I 21 are connected in parallel with the winding I38 in the oscillator grid circuit as the various switches I28 are closed for preselection tuning.

The feedback winding I3! is also coupled with a second winding I30 for the grid circuit of the oscillator, and the latter is efiected as the oscil- -lator inductance in the broadcast band when variably tuned by the capacitor I33, the connection with the movable contact element I30 being eiiected through a fixed contact I40 for the inductance winding I39.

The details of the oscillator circuit per se, as shown in Fig. 2, do not form part of this invention and are shown, described and claimed in a copending application assigned to the same assignee as this application.

It will be seen that in the rf or detector section of the switch, the contact I22 is provided for the variable tuning capacitor section I20, and a corresponding contact I32 is provided in the oscillator section SI for the oscillator variable tuning capacitor section I33. Also, in the rf or first detector switching section 90, the contact H9 is provided for the manual preselection or control circuit H8 and a similar contact I3I is provided in the oscillator section 9| for the manual tuning circuit I26. Since the tuning of the rf or first detector circuit is provided by the adjustable capacitors I I6, no change in the inductance switching is made for the variable tuning by the capacitor I20. The switching change includes merely disconnecting the circuit I I8 for the preselection system and connecting the variable tuning capacitor I20 with the contact element I01.

However, since the tuning of the oscillator is by means of adjustable inductances, the switching change also involves disconnecting the oscillator grid inductance I38 and replacing it in circuit by the tuning inductance element I39, in addition to disconnecting the preselection circuit I26 and making the variable tuning connection at the contact I32.

In each of the wave band switch sections, a movable grid circuit contact element is arranged to select not only connections for the various wave band inductances, but also to select for the grid circuit either connection with the preselection tuning circuit or the manually variable tuning circuit, thereby simplifying the switch operations and the switch construction.

It will be seen that all of the tuning elements I26 and II 6 are parallel connected to ground or chassis on one side, and through the selector switches I28 and III are connected to single control circuits. The switches for each channel are interconnected, as indicated by the dotted line connection I4I, so that the inductance change in the oscillator circuit and the capacity change in the r) circuit for each selected channel may be made simultaneously and instantly to change from one channel or broadcasting station to another. The mechanical connection between the operating portions of the switch sections 90 and-9| is diagrammatically represented by the dotted connection I42.

Since the preselection tuning elements involve a common ground return connection and only two circuit lead connections I26 and I I8, the parallel tuning elements may be placed in convenient positions on or near a receiver chassis, with the adjustable tuning elements grouped for facilitating operation and preselection adjustment. Since the two control circuits contain differing types of circuit tuning elements, namely, capacity adjusting elements for one circuit and inductance adjusting elements in the other circuit, the normal spacing when mounted being such as to render capacity coupling efiects negligible, undesired eifects from stray coupling are substantially eliminated. The preselection circuits, therefore, include a group of parallel connected circuit tuning elements for the signal selecting or detector circuit, all of which elements have electrical characteristics wholly unadapted for coupling with the plurality of circuit tuning elements for the oscillator which have differing electrical characteristics, whereby they may be related closely in a receiver chassis or tuning unit without shielding or additional complication and cost.

We claim as our invention:

1. In a radio signalling system, the combination with two tunable signal circuits, of means for tuning one of said circuits to a series of preselected frequencies comprising adjustable tuning capacitors and selector switch elements and a single control circuit for connecting said capacitors with said one tunable signal circuit, and means for tuning the other of said tunable signal circuits to a plurality of frequencies in prede termined relation to the tuning of said first named circuit, said last named means being associated with said tuning capacitors in a group with normal spacing to preclude capacity coupling effects therewith and comprising a series of adjustable tuning inductances whereby inductive coupling is prevented and selector switch elements conjointly operable with said first named selector switch elements and a single control circuit for selectively connecting said inductances in the other of said circuits.

2. In a superheterodyne radio receiving system, the combination with a tunable signal receiving circuit, of a plurality of adjustable capacitor elements for tuning said circuit to a plurality of predetermined frequencies, a tunable oscillator circuit, and means for tuning said oscillator circuit to a plurality of predetermined frequencies comprising a plurality of adjustable inductance elements selectively connectable with said oscillator circuit and each comprising an inductance winding having a movable tuning core element associated therewith to vary the inductance of said winding, said tuning elements being grouped to spacing limits precluding stray capacity coupling effects between said tuning elements whereby unitary adjustment of said circuits is provided without stray inductive coupling between the circuits and tuning elements thereof.

3. In a superheterodyne radio receiving system having a tunable signal receiving circuit and a tunable oscillator circuit, adjustable capacity means for tuning the signal receiving circuit and adjustable inductance elements for tuning the oscillator circuit whereby said tuning means for the signal receiving and oscillator circuits may to the limit of element-to-element stray capacity coupling, be associated without stray inductive coupling, thereby to provide a unitary arrangement for tuning adjustment, selective switching means for connecting said tuning elements one in each circuit in pairs, thereby to cause said sys tem to respond to signals at preselected frequencies, and means for indicating the condition of adjustment of the selective switching means.

4. In a superheterodyne radio receiving system, the combination with means for tuning said system in a plurality of differing wave bands and including a tunable sgnal receiving circuit, a tunable oscillator circuit and wave band change switch means for said circuits, of a plurality of adjustable capacitor elements for tuning the signal receiving circuit and a plurality of adjustable inductance elements for tuning the oscillator circuit, a pair oi. tuning control circuits, means in said wave band change switch means providing a connection with the signal receiving circuit and said capacitor elements in parallel through one 01' said control circuits, and a connection with the oscillator circuit and said inductance elements in parallel through the other control circuit, a selector switch element in circuit with each or said tuning elements, and means for operating said switch elements in pairs whereby the signal receiving and oscillator circuits are simultaneously tunable to receive signals in a plurality of differing signal channels in one wave band.

5. In a superheterodyne radio receiving system, the combination with a tunable signal receiving circuit having a high signal potential circuit lead and a grounded low signal potential circuit lead, a tuning inductance connected between said leads, an oscillator circuit having a high signal potential lead and a grounded low signal potential lead, a tuning inductance connected between said leads, a predetermined number of tuning capacitors each having an adjustable grounded electrode, a tuning control lead connected with the high signal potential lead of the signal input circuit, selector switch means for connecting each of said capacitors selectively with said tuning control lead, a plurality of tuning inductance elements corresponding in numher to the number of said capacitors each comprising a winding grounded at one end and having an opposite terminal end, a grounded movable core element for each of said windings for adjusting the tuning thereof, a second tuning control lead connected with the high signal potential lead of said oscillator circuit, and selector switch means conjointly operable with said first named selector switch means for connecting each of said terminal ends of said windings selectively with said second tuning control lead whereby said tuning capacitors and inductance elements together with said selectorswitch means may be provided as a unit and connected with said receiving system through said tuning control leads and ground.

6. In a preselection tuning system for a superheterodyne receiver, a plurality of adjustable tuning capictors for a signal input circuit of said receiver, a plurality of adjustable tuning inductances for the oscillator circuit of said receiver of the type comprising a winding having a movable core tuning element, said tuning capacitors and tuning inductances being arranged in spaced relation to each other for unitary tuning adjustment in one location in the receiver, and said tuning reactances being spaced and arranged in a group to have substantially no capacity coupling reaction one upon the other in the respective circuits whereby shielding for said tuning elements is eliminated without introducing stray inductive coupling therethrough between said signal input circuit and said oscillator circuit.

KENNETH A. CHI'I'IICK. MACK C. JONES. 

